Jesse Lackey wrote:

> I'd like to measure current into and out of the battery, the range is
> up to 400mA going in when charging, and out of will be brief pulses
> of 150mA when doing RF transmit and down to 50uA when in a sleep
> state.=20
>=20
> I'd also like to measure battery voltage to check the
> charge/discharge curves under different operational scenarios.=20
>=20
> So off the cuff, I'd say a 10 ohm sense resistor, ideally high-side
> but low-side is ok, with differential connection to an amplifier that
> feeds the A/D. =20

In a similar situation I used two switchable sense resistors. The
resistance of the switch doesn't really matter much if it isn't big
enough to make a difference in operation, and you get a much better
resolution on the sleep state current. (In my case I had regular
wakeups, still very low current, that I wanted to measure in addition to
the normal sleep current.)

You just need to make sure that you "make before break" on switching
over and really only have the bigger resistor in the line when the
device is sleeping, or else you'll trigger a reset.


> Software-wise, something to save data points (several a second would
> be nice, 100 a second would be great), draw graphs, and do basic math
> (total power consumed) would be nice.

I don't have any of those, but there are many USB-based data acquisition
devices out there that come with software that does something like this.
Probably export to CSV or Excel is good to have, for better and/or nicer
output processing.

Gerhard
--=20
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